macros: Use %{build_rustflags} convention

But keep %__global_rustflags around for compatibility.

Signed-off-by: Igor Gnatenko <ignatenkobrain@fedoraproject.org>

data/macros.rust

@@ -2,14 +2,16 @@
 %__rustdoc %{_bindir}/rustdoc
 
 # Enable optimization, debuginfo, and link hardening.
-%__global_rustflags %{shrink:
+%build_rustflags %{shrink:
   -Copt-level=3
   -Cdebuginfo=2
   -Clink-arg=-Wl,-z,relro,-z,now
   -Ccodegen-units=1
 }
 
+%__global_rustflags %{build_rustflags}
+
 %__global_rustflags_toml [%{lua:
-    for arg in string.gmatch(rpm.expand("%{__global_rustflags}"), "%S+") do
+    for arg in string.gmatch(rpm.expand("%{build_rustflags}"), "%S+") do
         print('"' .. arg .. '", ')
     end}]